Yeah, your call. It all depends on the paint. Sometimes PP leaves a ready-to-wax finish (especially if you fully break down the abrasives) and sometimes you'll notice an improvement following up with the MP.
On silver Audis, for instance, I always follow with MP, but a friend of mine (with the same paint on his wife's car) never does, he just goes straight from PP to his LSP. It's not like their car is all micromarred up or anything, not that I've ever looked at it very closely.